Competition Dyno Question

[jaybigboy34]

The first time I dynoed, I had 428hp and 910ft. with my stock tires. My question is will I lose hp and ft. on the dyno since I have 325/70/18 tires on my truck now? Also, my truck made the highest numbers in 6th gear. Will that still be the case with the bigger tires, or do I need to dyno in a lower gear?



Thanks

 

[jaybigboy34]

Come on now. I know someone can help me out.

 

[RustyJC]

It all depends. Are you running on an inertial or a load (eddy current, water brake, etc. ) dyno? If you're running on an inertial dyno, the greater inertia of larger wheels and tires may leave less power available to accelerate the rollers which will drop horsepower/torque readings somewhat. On a load dyno, being more steady-state, larger wheels and tires shouldn't matter as much.



On an inertial dyno, my experience says make the run in the highest gear possible since this "tricks" the engine into thinking the rollers have more inertia and will load the engine more, helping turbo spoolup, etc. I made around 325/650 on a Dynojet 246C with 2 pulls in 5th as opposed to 347/762 with 2 pulls in 6th. On a load dyno, I'd run in 5th (direct) to minimize drivetrain losses.



Rusty

 

[mattymac]

Was it a load or inertia dyno? That will make a diffrence with tire size. If you got more in 6th I would say it sounds like an inertia. If thats the case then I would say your bigger tires may help your #'s since most cant load the truck enough to make full boost and max power. Bigger tires= more load, and boost.



You beat my post Rusty!

 

[jaybigboy34]

I dynoed on the dynoject 246c like you did, so are the bigger tires going to hurt me or help me?

 

[Reb.B]

with the dyno jet you need all the load you can get. Dyno in O/D with the biggest tires. The net HP will be higher, enev though it takes more power to turn larger, heavier tire and in O/D. The slower and the more air the turbo makes the greater the result will be, the faster the turbo the closer the number will come out between O/D and drive.

 

[RustyJC]

I dynoed on the dynoject 246c like you did, so are the bigger tires going to hurt me or help me?

That's a very interesting question. With a stock turbo, I've seen any number of individuals state that larger wheels and tires cost them hp/torque on the Dynojet. With a larger single or twin turbos, however, the scenario described by the others may well be valid - the power gained by the improved turbo spoolup due to the higher inertial load of the large tires could potentially more than offset the increased inertial losses of the larger tires and wheels.



Rusty

 

[Reb.B]

i've never seen a loss. I've seen as little as 4 HP gain on fast turbos and as much as 70 HP gain on a big set of twins

 

[DavidTD]

My experience tells me that in general until you reach a big tire (40"+) that the power loss is minimal. But remember, larger tires are more rotating mass and it will cost you hp, kinda the point of measuring the power at the wheels.